During wafer testing, electrical contact is preferably made between tester channels or power supplies and the bondpads (also known as pads or pins) of the one or more dies (AKA devices) being tested by means of a probecard. The probecard is constructed with a multitude of metallic probes that are attached to a printed circuit board. The traces of the PC board are electrically connected to tester channels and power supplies, while the probes, often in the format of tungsten needles, make temporary contact to the surface of the bondpads. The metallic “probes” provide a mechanical and electrical interface through which electrical signals and power supply voltages are applied to the device during testing, and also pass voltage responses from the device back to the tester for evaluation. Each device on a wafer will contain multiple bondpads (sometimes, hundreds per die), and in some cases (during parallel test operations), multiple devices at a time will be probed. Therefore, a probecard may have as many as several thousand probes in the probe array, spanning an area of several centimeters. During a sequential test operation, each die is tested separately. During a parallel test operation, a subset of all of the dies on a wafer, or all of the dies on the wafer, are tested simultaneously. Therefore, depending on the testing conditions, one or several passes may be made through the wafer in order to contact and to test all of the dies on the wafer. Each pass is referred to as a “touchdown”.
For each touchdown for each wafer during wafer testing, each probe in the probe array should be aligned to fall on the correct corresponding bondpad. Note that alignment relates to any of the X dimension, the Y dimension, the Z-dimension (for probe array planarity), and/or rotationally (so called “theta dimension”, referring to the angular dimension).
If an alignment problem remains undetected and worsens, the integrity of the electrical signals involved in testing dies on a wafer may eventually degrade to a point in which spurious failures of dies being tested appear. Additionally or alternatively an alignment problem may cause a loss in yield due to mechanical damage of die bondpads. Additionally or alternatively, after probing in a misaligned condition, the probecard may require special cleaning and/or other maintenance (for example due to having probed on the insulating layer typically surrounding the bondpads). Additionally or alternatively, an alignment problem may cause a requirement for wafer(s) to be reprobed (for example due to invalid yield loss) which may necessitate special handling and may consume manufacturing capacity.
Similarly, during testing of packaged devices (“units”), electrical contact is preferably made between tester channels or power supplies and the “pins” of a packaged device. The term “pins” is commonly used to refer to the external package contact point that is electrically connected to the die bondpads, internal to the package. (Note that each packaged device may include one or more die). A packaged device is inserted into a socket which is mounted on a loadboard. The traces of the loadboard are electrically connected to tester channels and power supplies, and the loadboard also provides a rigid surface to physically support the socket. The test socket contacts, make temporary contact to the surface of the pins of the packaged device. The metallic test socket contacts provide a mechanical and electrical interface through which electrical signals and power supply voltages are applied to the packaged device during testing, and also pass voltage responses from the packaged device back to the tester for evaluation. Each packaged device may contain multiple pins (sometimes, hundreds per device). During a sequential test operation, each packaged device is tested separately. During a parallel test operation, a plurality of packaged devices may be tested in parallel in a plurality of sockets and the handler may perform the socketing and unsocketing of the plurality of packaged devices in parallel.
During testing each test socket contact should be aligned to fall on the correct corresponding pin. Note that alignment relates to any of the X dimension, the Y dimension, the Z-dimension, and/or rotationally (so called “theta dimension”, referring to the angular dimension).
If an alignment problem remains undetected and worsens, the integrity of the electrical signals involved in testing packaged devices may eventually degrade to a point in which spurious failures of packaged devices being tested appear. Additionally or alternatively an alignment problem may cause a loss in yield due to mechanical damage of pins. Additionally or alternatively, after socketing/unsocketing in a misaligned condition, the test socket may require special cleaning and/or other maintenance. Additionally or alternatively, an alignment problem may cause a requirement for packaged devices to be resocketed (for example due to invalid yield loss) which may necessitate special handling and may consume manufacturing capacity.